Interactions between protein subunits are almost ubiquitous in biological systems. Three different aspects of subunit-subunit interactions will be studied: A. The interactions between the side chains of the amino acid residues at the contact interface are entirely analogous to the interactions within a protein. These experiments can thus provide information pertaining to dynamics of protein folding. B. The form of large structures provided by the spontaneous self-assembly of subunits is determined by the local interactions. Mechanistic studies can reveal how this process is controlled. C. Cooperative phenomena occur in some multisubunit systems. Exploring the kinetics of interactions at the interface can reveal how information is communicated from one subunit to another. A novel pressure relaxation instrument will be used in monitoring the kinetics of such interactions. These studies will provide basic information pertaining to a host of physiological and pathological processes.